The technical scope of the invention is that of devices linking a case and a projectile and more particularly devices allowing a combustible case and a large caliber projectile (caliber of over 45 mm) to be linked together.
Such a device is known by patent EP-0307307 that comprises a sealing band incorporating a rear skirt linked to the case and providing low pressure sealing (pressure of around a few MPa) and a front rib housed in a groove in the projectile and providing high pressure sealing (pressure of around several hundred MPa), such as is the case in a classical band.
Low-pressure sealing is essential in the first few tenths of milliseconds following the ignition of the propellant charge contained in the combustible case. Indeed, the containment provided by such a case is less than that obtained using a metallic case and the displacement of the projectile occurs at a lower pressure. Sealing that is not sensitive enough to be operational from the point of ignition is likely to allow gases to escape towards the front of the projectile, thereby reducing the efficiency of the propellant charge.
Such a device, however, has certain drawbacks.
The case is generally fastened by riveting its skirt, which is integral with the band.
The fracture of the skirt when passing through the forcing cone of the weapon leads to a reduction in the effective width of the bard. This results in a reduction in the firing capacity of the projectile in worn barrels.
Moreover, the mechanical loads and stresses received by the munition are transmitted to the band whose gas-tightness properties are likely to be deteriorated, thereby leading to dispersion from a ballistic point of view.
The aim of the invention is to propose a device to link a case and a projectile that does not suffer from such drawbacks.
Thus, the device according to the invention provides for simple reliable attachment whilst increasing the effective length of the band, thereby improving sealing, even for firing from worn barrels.
Thus, the subject of the invention is a device to link a case and a projectile carrying a sealing band having a rear skirt providing low pressure sealing and a front rib housed in a first groove i n the projectile, such device comprising a ring having a flared rear part intended to be made integral with the case and a front part made integral with the projectile by attachment means, wherein the front part of said ring is housed between said rear skirt of said band and said projectile and has a lip co-operating with said first groove or with a second groove in the projectile.
According to a first embodiment, the lip is housed in the first conical-bottomed groove, the tip of the cone being placed on the side of a rear part of the projectile.
The front part of the ring can abut against an inner profile of the band.
The front part of the ring can incorporate an external profile that will co-operate with a matching profile on the band.
According to a second embodiment, the device also prevents the band from being subjected to mechanical stresses transmitted by the projectile or the case.
Such a result is obtained by providing separate first and second grooves.
Advantageously, the front part of the ring will be housed in a second groove and can incorporate at least one inner fluting arranged along a generating line and allowing the gases to pass through the ring up to the band.
According to one variant, at least one fluting can co-operate with an obstacle, such as a pin or a peg, integral with the projectile, such a co-operation enabling the ring and the projectile to be joined together in rotation.
The front part of the ring can incorporate an abutment surface able to co-operate with a matching rear surface of the band, a first play existing between these two surfaces when the band and the ring are in their respective grooves.
The ring can incorporate an inner counter-sink forming an abutment and intended to co-operate with an abutment surface on the projectile, a second play existing between said counter-sink and the projectile, the second play being greater than the first play.
A further aim of the invention is to propose a process to mount, a band onto a projectile, said process being simpler and less expensive that the known process described notably in patent EP-0307307.
According to said patent the band/linking part is fastened to the projectile by injection around the projectile.
Such a process requires the bands to be produced directly on the sabots thereby complicating the production process.
The process according to the invention allows the linking part and band to be produced independently of the sabot. Assembly is only carried out at a later stage. Production is thereby simplified and its cost reduced.
Thus the process according to the invention to mount a band onto a projectile is characterized in that the band and linking ring are made to slide along the projectile in a single operation, the ring pushing the band until both ring and band are clipped into their respective grooves.
Both ring and band can be made of a plastic material and the ring and band will be heated before being put into place.